1. Field of the Invention
The present invention relates to a printer driver, especially a printer driver that is implemented as software rather than as hardware. More particularly, the present invention relates to a circuit and a method for converting printing data in a printer driver.
2. Description of the Related Art
A printer driver may be used when a computer user desires to print out a letter or an image information by way of a printer while working on a computer application program. Often, such a printer driver is a software program which is designed such that the application program may control a printer, even when the printer has atypical hardware and internal control commands. This is useful because each printer may employ a different operating method, a different code, and a different command system for each special printer functions. With use of the printer driver, however, the application program may properly control any types of printers in spite of these differences.
In recent times, GUI (Graphic User Interface) provides a unique printer driver. In such a printer driver, GUI gives a graphic icon for the printer control command. Therefore, it is not necessary that an application program utilizing the GUI should include a separate printer driver. The challenge is to provide an ever more effective use of the printer driver, especially as to the effective handling of memory. An exemplar of the contemporary art on this matter is Miyazaki (U.S. Pat. No. 5,587,800, Image Processing Method And Apparatus, Dec. 24, 1996) discussing a page printer storing form data received from a host computer into a RAM before printing output. In the case where the respective cache memories are full, the pattern of the lowest access frequency among registered patterns is deleted, thus realizing effective use of cache memories. Gretter (U.S. Pat. No. 4,882,686, Printing Apparatus With Improved Data Formatting Circuitry, Nov. 21, 1989) discusses an integrated circuit memory chip having sufficient buffer memory sites for storing either a full line of image signals to be printed or image signals sufficient for filling more than one shift register assemblage associated with the recording element driver. Image signals are read from the memory chip to the intermediate register in a non-consecutive sequential order. Arai (U.S. Pat. No. 5,008,685, Laser Generator For Producing Modulating Data Therefor, Apr. 16, 1991) discusses a laser generating apparatus inputting a laser scanner as modulating data signal indicative of the logical sum of serial data corresponding to image formation and an arbitrarily delayed version of the serial data. Yoshida et al (U.S. Pat. No. 5,068,676, Image Data Storing Device For An Image Forming Apparatus, Nov. 26, 1991) discusses an image data storing device for an image forming apparatus having a multitude of line buffers to which image data are written from external equipment and from which the written image data are read to form an image. During an image forming period, the selectors condition each of the line buffers for one of three different states while, during a non-image forming period, they hold the line buffers in individual states. This allows the line buffers to start operating under the same conditions whenever an image forming period is reached. Yamada (U.S. Pat. No. 5,473,359, Image Forming Apparatus, Dec. 5, 1995) discusses a laser beam printer apparatus which can add printing data after bit map image data is expanded to printing data. Such additional printing data is synthesized with printing data at a predetermined period on basis of a clock supplied from either a main controlling unit or an image forming section. Murakami et al. (U.S. Pat. No. 5,548,321, Optical Scanning Apparatus For Scanning Laser Beam On Imaging Surface And Recording Image Data On Imaging Surface In Units Of Dots, Aug. 20, 1996) discusses an optical scanning apparatus. In accordance with the operation of an address counter, a bus switching circuit selectively reads out dot width data of a pattern different from a preceding pattern from the memory for each scanning operation, and outputs the data to a latch circuit. Miura et al. (U.S. Pat. No. 4,729,038, Recording Apparatus Capable Of Forming A Shadow Print Impression To Characters, Mar. 1, 1988) discusses a laser recording apparatus. Line memories are utilized to store data therein, and examined to determine any change of stored data from non-character data to character data whereupon a shadow printing operation is also preferred. From my study of these contemporary practices and the art, I have found that there is a need to convert printing data into bit map data that can be processed at a printer when the quantity of the printing data exceeds the storage capacity of a memory for storing the printing data.